Press Releases
Jun. 6, 2011

Optical switching magnet composed of iron ion and organic molecule

— Discovery of light-induced Spin-crossover magnet —
Presenters
  • Shin-ichi Ohkoshi (Professor, Department of Chemistry, School of Science, The University of Tokyo)
  • Hiroko Tokoro (Assistant professor, Department of Chemistry, School of Science, The University of Tokyo)
  • Kenta Imoto (Doctor course 1st year, Department of Chemistry, School of Science, The University of Tokyo)
  • Yoshihide Tsunobuchi (Assistant, Department of Chemistry, School of Science, The University of Tokyo)
  • Shinjiro Takano (Master course 1st year, Department of Chemistry, School of Science, The University of Tokyo)

Abstract

Research group of Prof. Shin-ichi Ohkoshi (Department of Chemistry, School of Science, The University of Tokyo) reported that they discovered a new type of photomagnet which shows transition from paramagnet (nonmagnetically ordered phase) to ferromagnet (magnetically ordered phase) by the blue light irradiation. The photomagnetic phase shows a ferromagnertic phase transition temperature of 20 K, which is caused by light-induced spin-crossover phenomenon, and returns to the original paramagnetic state by thermal annealing. This material is composed of iron ion, niobium ion, organic molecule, and cyano group. This light-induced spin-crossover magnet contains a lot of organic molecules and this may be the first step toward flexible optical-magnetic material.

Paper information

The paper concerning to the present study was published in ‘Nature Chemistry’ (Advance online publication) at 18:00 pm on 5th June 2010 (UK time).

Title:
Light-Induced Spin-crossover Magnet
Authors:
Shin-ichi Ohkoshi*, Kenta Imoto, Yoshihide Tsunobuchi, Shinjiro Takano, and Hiroko Tokoro.
Figure 1

Figure 1. Schematic illustration of spin-crossover phenomenon and spin-crossover photomagnetism. In iron(II) spin-crossover phenomenon, the electronic state changes between high spin state FeII (S = 2) and low spin state FeII (S = 0) by thermal energy or photo irradiation. When infinite numbers of light-induced HS sites are magnetically ordered, bulk magnetization should be observed.

Figure 2

Figure 2. Crystal structure of Fe2[Nb(CN)8]·(4-pyridinealdoxime)8·2H2O. (a) Coordination environments around Fe and Nb. The Fe is coordinated by two cyanide nitrogen atoms of [NbIV(CN)8] and four pyridyl nitrogen atoms of 4-pyridinealdoxime. The four CN groups of [NbIV(CN)8] were bridged to four Fe, and the other four CN groups were free. Red and green ball-sticks represent [FeN6] and [NbC8] moieties, respectively. Light blue, pink, and blue balls represent C, N, and O atoms in 4-pyridinealdoxime. (b) Cyano-bridged Fe-Nb 3-dimensional framework viewed along the c-axis.

Figure 3

Figure 3. Mechanism of light-induced spin-crossover ferromagnetism. (a) Schematic illustration of light-induced spin-crossover of FeII. The 1A1 state on FeII(LS) transited to the excited singlet state 1T2 (or 1T1) due to light irradiation, and then partially proceeded to the metastable quintet state 5T2 through the triplet states of 3T2 and 3T1. (b) Schematic illustration of ferrimagnetic ordering between NbIV (S = 1/2) and FeIIHS (S = 2) due to a light-induced spin-crossover. In the photo-induced phase, the magnetic spins on the photo-produced FeII(HS) (S = 2) and neighboring NbIV (S= 1/2) interacted antiferromagnetically by a strong superexchange interaction (Jex) through the CN ligand, resulting in spontaneous magnetization. Black bars inside the spheres represent the levels of 4d orbitals on NbIV or 3d orbitals on FeII. Red and green arrows represent spin.